A novel monolithic beam steering high power transmitter for low cost free space optical wireless links

A novel transmitter for directed-beam infra-red wireless that utilizes a combination of both gain-guiding and index-guiding mechanism to ameliorate the shortcoming of the state-of-the-art technology is proposed and demonstrated. The 3mm long tapered laser consists of an index-guided ridge straight section and a gain-guided tapered section with a full angle of 6 degrees. By implementing multiple contact with a sufficiently high inter-contact resistance, discrete switching between different angles can be obtained by selectively pumping current to different contact (gain-guiding effect), while fine-tuning of a given angle can be achieved by adjusting the injection current of nearby contacts (index-guiding effect). The tapered laser's metal cover is removed using focus ion beam etching technique to form three separate sections: base section as filter, left section and right section for beam steering. The device is biased by current pulses of 1 mu s width and 0.1% duty cycle. With a 1.6A injection current, an output power of 2W is achieved, which would be suitable to overcome large free space optical loss and facilitate the use of transmitting methods. The beam profile steered by 3.2 degrees and -5.4 degrees from the central lobe when injection cur-rent is limited to the left and right section respectively is measured. It is also observed that as injection cur-rent increases, the beam profile is steered towards the central position. This is because as the injection current increases, the local refractive index is decreased, thereby shifting the beam profile towards the opposite direction.